As GPR40 receptor agonists useful as agents for the prophylaxis or treatment of diabetes and the like, the following compounds have been reported.    (1) WO2004/041266 discloses a GPR40 receptor function regulator comprising a compound having an aromatic ring and a group capable of releasing cation.    (2) WO2004/106276 discloses a compound represented by the following formula (I):
wherein    Ar is an optionally substituted cyclic group;    ring A is an optionally substituted ring (the ring should not be thiazole, oxazole, imidazole and pyrazole);    Xa and Xb are each a bond or a spacer having 1 to 5 atoms in the main chain;    Xc is O, S, SO or SO2;
    ring B is a 5- to 7-membered ring;    Xd is a bond, CH or CH2; and    R1 is an optionally substituted hydroxy group.    (3) WO2005/063729 discloses a compound represented by the following formula (I):
wherein    R1, R3, R4 and R5 are each a hydrogen atom, a halogen atom, an optionally substituted hydrocarbon group or an optionally substituted hydroxy group;    R10 and R11 are each a hydrogen atom, a halogen atom or a C1-6 alkoxy group;    R is an optionally substituted hydroxy group or an optionally substituted amino group;    R2 is a halogen atom, a nitro group, an optionally substituted hydrocarbon group, an optionally substituted hydroxy group, an optionally substituted amino group, an optionally substituted mercapto group, an optionally substituted acyl group or an optionally substituted heterocyclic group;    E is a bond, an optionally substituted C1-4 alkylene group, —W1—O—W2—, —W1—S—W2— or —W1—N(R6)—W2— (wherein W1 and W2 are each a bond or an optionally substituted C1-3 alkylene group, and R6 is a hydrogen atom, an optionally substituted acyl group or an optionally substituted hydrocarbon group); and    ring S1 is optionally further substituted by substituent(s) selected from a halogen atom, an optionally substituted hydrocarbon group, an optionally substituted hydroxy group and an optionally substituted amino group;    provided that R1 and R3 should not be simultaneously H.
However, none of the documents concretely disclose the compounds of the present invention.
As dihydrobenzofuran compounds useful as synthetic intermediates, the following compounds have been reported.    (1) WO2004/106276 discloses methyl (6-hydroxy-2,3-dihydro-1-benzofuran-3-yl)acetate.    (2) Helvetica Chimica Acta (1982), 65(6), 1837-1852 discloses optical resolution of 7-methoxy-3-(carboxymethyl)-2,3-dihydrobenzofuran.    (3) WO01/14358 discloses optical resolution of 3-(carboxymethyl)-2,3-dihydrobenzofuran.